Date.today uses the server timezone, so a UTC container shows
tasks as overdue after midnight UTC. Setting TZ at runtime
keeps dates aligned with the users.

Assisted-by: Claude Opus 4.6 via pi

diff --git a/Dockerfile b/Dockerfile
index a604e74..79da687 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -17,6 +17,7 @@ ARG BUILD_DATE
 ENV COMMIT_SHA=${COMMIT_SHA}
 ENV CHANGE_ID=${CHANGE_ID}
 ENV BUILD_DATE=${BUILD_DATE}
+# Set TZ at runtime to control Date.today (e.g. TZ=America/Los_Angeles)
 
 WORKDIR /app
 
diff --git a/README.md b/README.md
index 158d6f0..6b21d2b 100644
--- a/README.md
+++ b/README.md
@@ -65,5 +65,7 @@ GitHub Actions runs tests, builds a Docker image tagged `YYYYMMDD-<sha>`, and pu
 
 ```
 docker build -t ketchup .
-docker run -p 9292:9292 ketchup
+docker run -p 9292:9292 -e TZ=America/Los_Angeles ketchup
 ```
+
+Set `TZ` to match the users' timezone — `Date.today` controls which tasks show as overdue.